Now checking for RunProgress hook in call instead of in the constructor
Interval hook and time function now class attributes not parameters

It is not possible to parameterize AttrTree instances that also pickle
correctly as the __setstate__ implemented by param uses __setattr__
before the object is fully initialized.
Custom path elements of an AttrTree must now be capitalized
Fixed misleading variable names referencing previous names of AttrTree
Fixed iteration on NdMapping to work properly with CoordinateGrids
Now using US English spelling for method 'analyze'
Improved granularity of Exceptions and improved exception messages
Added 19 unit tests of AttrTree and ViewRef
Improved variable names in ViewRef doctest